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Old November 6, 2009, 02:21 AM   #1
Gregory Gauvin
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Join Date: March 6, 2009
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Minor Loads

I have heard that the .40 SW loaded to minor power factor in the 165 and 180 grain loads recoil less than the 9mm 124 grain loads loaded to minor.

In any case, what velocity can I run 155 grain loads in the 40 to simulate 9mm recoil? I've run 155 grainers at 1050 FPS and they have more than enough umph to cycle the action. I was wondering what velocity would simulate the recoil of hot 124 or 127 grain 9mm defense ammunition and what velocity might simulate some standard loadings.

If I could pop the 155 grainers at 900 FPS would that recoil about as much as a 124 standard load?
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Old November 6, 2009, 08:09 AM   #2
SL1
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You can calculate the recoil momentum by multiplying the bullet weight by the muzzle velocity, which is what the "Power Factor" is attempting to do for the various action pistol sports. (Thre are various constant "conversion factors" to put momentum in standard engineering units, but we can neglect those for making comparisons.) To make the calculation a little more accurate, you can add the powder weight mutliplied by 4700 fps, which is intended to account for the "rocket effect" when the powder gases accelerate out of the bore after the bullet leaves. This velocity factor for the power weight probably varies according to something like muzzle pressure, but I have never seen anything published about that, and haven't tried to figure it out for myself.

Of course, the weight of the gun also makes a difference in what you feel when you are holding it as it goes off. If you are shooting the different cartridges in different guns, you can even things out by dividing by the weight of the gun. That would give you a theoretical "free recoil velocity" of the gun, which is the speed that it would be coming back at you if you were NOT holding it.

But, you ARE holding it, and that makes a lot of difference. Instead of coming back at you at the calculated velocity and your hand-wrist-arm-shoulder-whole body absorbing it after it has gotten up to speed, what actually happens is that the various parts of your body absorb the push as it is building-up, and the gun never reaches the calculated velocity. (It's like the difference between holding a shotgun tight against your shoulder vs pulling it slightly off your shoulder when you fire it; the gun DOES get up to its calculated velocity if it isn't against your shoulder, and it HURTS when it does get to your shloulder!)

So, in the end, recoil that you "perceive" is not what you can calculate. Light bullets that with a high muzzle velocity seem "snappier" and heavy bullets with lower muzzle velocity seem "softer" when their muzzle velocities are adjusted to have the same momentum ("power factor"). It has to do with the rate of acceleration of the gun, which depends on the rate of acceleration of the bullet, and, in an auto-loader, on the rates that other things accelerate and decelerate, like the slide.

Some folks like "snappy" and say it feels like less recoil for them, while others like "soft" and say it feels like less recoil to them. The consensus seems to be that you need to try them both to see how they feel to YOU. I don't know for sure, but I suspect that it has a lot to do with exactly how the various parts of each person's body actually flex to absorb the recoil, as well as how each person's mind perceives that flexing.

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